The present invention relates to an electrical cable and a method and equipment for reducing its coefficient of friction.
Electrical cables which include at least one conductor core and at least one coating are well known.
Said cables present the disadvantage that their exterior surface has a high coefficient of friction, so that they are awkward to fit in internal sections of walls and ceilings, since when they come into contact with the adjacent surfaces (pipes, cables, etc.) they become stuck.
In order to overcome said difficulty, alternative materials such as vaselines are currently used to coat the exterior surface of the cable, thereby reducing the coefficient of friction.
In a complementary manner, guides of small diameter are also used, one end of which is inserted through the cavity through which the cable has to pass and the other is attached to the end of the cable which must be inserted into the cavity. Thus, once the guide has emerged at the desired place it is pulled until the end of the cable appears again after having passed through the entire section.
Whatever the method used, the installation of said cables involves a considerable loss of time and an economic cost, since alternative materials are required.
With the method, the cable and the equipment of the invention said disadvantages can be solved, while providing other advantages which will be described below.
The method for the manufacture of electrical cables is characterized in that it includes a step in which a lubricating material is sprayed onto the surface of the cable.
A cable with low coefficient of friction is achieved thereby, so that subsequent installation of the same is considerably simplified, since it slides over the surfaces with which it comes into contact. It also means a clear economic and time improvement, as no type of alternative materials are required for installing it.
According to one characteristic of the invention, the spraying step is carried out between the step of coating the conductor wire with plastic material and the step of cooling said material.
This position of the spraying step in time is important since, when the conductor wire is coated with the plastic material, said material is in a state of fusion (approximately 150xc2x0 C.), the high temperature of which causes volatilization of the solvents present in the lubricating material, which means that there is greater adherence of said lubricating material on the surface of the plastic material. The subsequent cooling (down to approximately 20xc2x0 C.) of the plastic material together with the lubricating material leads to drying of the surface, leaving the two materials bonded to form a coating of low coefficient of friction.
Suitable lubricating material can involve the use of a fluorated organic resin, such as a polymer of one or more fluorated monomers selected from amongst, for example, tetrafluoroethylene, vinylidene fluoride, chlorotrifluoroethylene and the like. The use of polytetrafluoroethylene (PTFE) is particularly preferable. The fluorated resin is preferably used in the form of an emulsion or aqueous dispersion.
The electrical cable is characterized in that it incorporates a lubricating material on the exterior coating, which lubricating material is applied by spraying.
The exterior coating of the cable is thus well impregnated with said material, forming a fine layer on the plastic material, since it emerges at high pressure and the plastic material is at high temperatures.
The equipment for the manufacturing of electrical cables is characterized in that it includes a device for the application of a lubricating material on the surface of the cable.
Said device includes a box section through which the cable passes, a plurality of nozzles for spraying the lubricating material mounted inside the box section, a tank for said lubricating material, and a pressure pump to carry the lubricating material from the tank to the spraying nozzles.
Moreover, the device also includes a pressure adjusting valve, a level indicator of the lubricating material tank, and a pressure gauge.